1. Field of the Invention
The invention relates to diagnosis and treatment of soft tissue pain. More particularly, the invention is a method and apparatus for measuring responses of soft tissue subject to acoustic stimulation, processing the response, and interpreting the response to indicate the location of stress and/or injury in soft tissue and for verifying the effectiveness of treatment of soft tissue.
2. Description of the Related Art
Existing techniques for diagnosis of the source of pain in soft tissue are relatively subjective and inaccurate. Typically, clinicians rely upon responses to patient questionnaires, medical histories, and subjective observation to diagnose the source of pain in soft tissue. These tools are inherently imprecise even when used in a meticulous manner. Several expensive technologies have been applied to diagnosis of the source of soft tissue pain. For example, magnetic resonance imaging (MRI), x-rays, and computerized tomography (CT) are known noninvasive technologies. Invasive technologies include nerve blocks, probes, and the like. Even when utilizing these technologies, results are frequently inaccurate or inconclusive. Multiple studies have shown that x-rays have little value in routine examination of the source of soft tissue pain. Even MRI is now only rarely recommended in back pain, since surgery based on such imaging has had a high failure rate. Moreover, the demonstration of abnormal scans and x-rays in people who lack back pain symptoms casts serious doubt upon the value of these technologies in soft tissue diagnosis.
Other diagnostics have little value in diagnosing the source of soft tissue pain. Nerve conduction studies and electromyography are indicated for detection of nerve damage only at advanced stages. Measurement devices for indicators of tissue mobility or tension are limited in scope and applicability. Ultrasound may image large muscle tears and can depict certain tissue, but not specifically pain or stress in tissue. Nerve blocks may identify an area of pain but are not suited for routine evaluation because skilled administration of injected anesthetic agents are required and risk factors are elevated. Blood flow analyses also have limited relevance to soft tissue pain.
Serum and saliva analyses for substances associated with pain have been used to diagnose the source of pain. However, protocols, norms, and standardization of sampling and processing techniques have yet to be established for such analyses. One theory is that visualization of chronic neck-shoulder pain can be achieved through the quantification of lowered microcirculation. However, this quantification requires the insertion of optical laser-Doppler single-fibers into two muscle sites concurrently with increased static contraction using electromyography. Of course, this method, even If proven to be accurate, is painful and has a high risk factor.
It is known to use acoustic energy to determine physical properties of various nonliving materials. Also, acoustic energy has been used In various medical applications. For example, U. S. Pat. No. 5,795,311 discloses an apparatus for treating tissue by imparting acoustic energy thereto. U.S. Pat. No. 5,458,130 discloses an apparatus which applies ultrasonic energy for measuring bone density, and strength, and for treating musculoskeletal tissue using a complex signal generator and processing system. U.S. Pat. No. 4,509,524 discloses a device for characterizing tissue based on reflected ultrasonic waves. U.S. Pat. No. 4,819,621 discloses an apparatus for detecting cavitation in tissue injuries by detection of a reflected acoustic signal. U.S. Pat. No. 4,216,766 discloses an apparatus for treating tissue by applying acoustic energy at the resonant frequency of a gas filled cavity surrounding the tissue to be treated. U.S. Pat. No. 5,115,808 discloses an apparatus for measuring the velocity of acoustic signals in tissue for determining the shear elastic properties of the tissue. U.S. Pat. No. 5,545,124 discloses a method for alleviating pain by charging tissue with acoustic shockwaves. However, the prior art does not permit reliable detection of stress in soft tissue through noninvasive measures. Accordingly, the prior art fails to provide a method or apparatus for diagnosing the source of pain due to soft tissue damage or stress.
Therefore, a vast area of difficult and often intractable syndromes of pain defy quantification and thus are difficult to treat in a reliable manner. Conventional diagnostic investigation often yields limited or equivocal findings, and involves expensive, painful and indirect methods. It follows that, therapeutic measures are compromised by this lack of resources.
The phrase “soft tissue” as used herein includes muscles, ligaments, connective tissue and fascia, nerve and blood vessel walls, and other essential structures of the body. Diagnostic designations relating to these tissues include chronic pain, strain, musculoskeletal pain and injury, myofascial pain and injury, benign, non-malignant, or idiopathic pain; myalgia, fibrositis, or fibromylalgia; repetitive strain injury (RSI) or overuse injury, including carpal tunnel syndrome (CTS), epicondylitis, tennis elbow, bursitis and tendinitis, temporomandibular joint disorder (TMD or TMJ), orofacial and neck pain, several types of headache, pelvic pain of unknown etiology, and back pain (all of which are included in the classification of “soft tissue pain” as used herein). The onset of soft tissue pain may have had an identifiable traumatic component but the duration of the pain often far exceeds the expected physiological process of recovery. Gross damage and disease processes are often absent with soft tissue pain.
The economic impact of soft tissue pain is reported by such studies as those of the annual combined cost of back pain-related medical care and disability compensation, which alone may reach $50 billion annually in the U.S. Back pain affects about 31 million Americans, is the leading cause of activity limitation in young adults, and generates annual U.S. productivity losses in the range of $28 billion. Incidence of tension-type headaches has been reported as high as 48.9%, with numerous annual lost workdays and days of decreased effectiveness at work, home, or school. Neck pain occurred at a 34% rate in one study. These statistics are representative of the magnitude of the of soft tissue pain which is severely hampered by lack of efficient diagnosis. It is frequently difficult to differentiate between specific conditions which benefit from surgery and those which do not. Despite due care in evaluation, surgery fails a significant percentage of patients who do not obtain relief and whose condition may even worsen. Conversely, surgical interventions performed for non-pain reasons are themselves a recognized cause of chronic soft tissue pain which is difficult to identify.